1. Field of the Invention
The present invention relates to a contact material for a vacuum valve whereby a stable voltage withstanding characteristic is obtained.
2. Description of the Related Art
Conventionally, the three basic characteristics required by a contact material are anti-welding interrupting characteristics, voltage withstanding characteristics and current interrupter characteristics; additionally, low and stable temperature rise characteristics and contact resistance characteristics are important requirements.
However, since some of these requirements are contradictory, it is not possible to satisfy all the requirements by metal of a single type. For this reason, in many of the contact materials that are practically employed, two or more elements are used in combination in order to mutually compensate for each others' deficiencies and contact materials for special applications such as large current or high voltage are being developed; some of these have excellent characteristics in their own way. However, the present situation is that no vacuum valve contact material has yet been obtained that fully satisfies increasingly severe requirements in terms of high voltage withstanding characteristic and large current interrupter characteristic.
In recent years, for example Cu (copper) or Cr (chromium) contacts, which have excellent voltage withstanding characteristics, have come to be chiefly used in ordinary circuit breakers in order to satisfy such demands. Methods of manufacturing CuCr contacts include the solid-phase sintering method comprising mixing Cu powder and Cr powder, forming and sintering, the infiltration method, in which manufacture is effected by infiltrating Cu into a Cr skeleton, and the arc welding method etc. Of these various methods of manufacture, the solid-phase sintering method is the most convenient method of manufacture, and has the characteristic advantage of enabling manufacture at low cost but, on the other hand, it was subject to the problem that the voltage withstanding characteristic was inferior.
As described above, the prior art is subject to the problem that contacts manufactured by the solid-phase sintering method, which is an inexpensive method of manufacture, are inferior in voltage withstanding characteristic.